The invention relates to spray pyrolysis, which involves forming a film by spraying onto a heated substrate an atomized solution containing the appropriate salts of the constituent elements of the film compound. The chemical reaction occurs upon spraying on the heated substrate, and the nonconstituent elements of the salts are removed by volatilization along with the solvent, typically water. For example, U.S. Pat. No. 3,148,084 discloses, along with other examples, the formation of CdS by spray pyrolysis, according to the following equation: EQU CdCl.sub.2 +H.sub.2 NC(.dbd.S)NH.sub.2 .fwdarw.CdS+volatile products
Before the conception of this invention Messrs. Steven A. Lis, Harvey B. Serreze, and Peter M. Sienkiewicz proposed the process claimed in a copending patent application (Ser. No. 231,127 filed Feb. 3, 1981) involving placing an agent directly in a spray solution to cause a variety of desirable oxidation/reduction reactions to occur when the spray solution contacted the heated substrate. Subsequently, but also before the conception of this invention, Michael R. Squillante suggested that highly soluble-organic acids would be desirable reducing agents, and improvements in the purity of the film compound were noted (Ser. No. 231,128 filed Feb. 3, 1981).